1. Field of Invention
The present invention relates to a touch panel, and more particularly, to a touch panel structure in which an effective active area of a touch panel is increased, sufficient linearity of equipotential lines is secured, and a voltage gradient and a voltage drop phenomenon are compensated.
2. Description of the Prior Art
Generally, touch panels are apparatuses installed in display units of information and communication equipment so as to input a variety of data or cause systems such as electronic/electrical equipment to execute specific commands, by merely getting a touch thereto or drawing characters or pictures thereon using a finger, a pen or the like. Since such touch panels can be used in systems such as the information and communication equipment or electronic/electrical equipment without using an input device such as a keyboard or a mouse, there is an advantage in that use of spaces can be maximized.
There are various kinds of touch panels. In a case where axes of a touch panel are configured by using a single sheet, a predetermined coordinate system should be constructed to correspond to physical signals inputted by a user. To this end, electrical coordinate signals are expressed by a touch panel with a two-dimensional coordinate system, and the coordinate system uses X and Y coordinates.
In order to define the X and Y coordinate system in the touch panel in such a way, a resistive surface of the entire sheet is constructed by a conductive film sheet with a constant surface resistance value and electrode segments are made of a material with a relatively low resistance value in order to generate an electric field for constructing the X and Y coordinates. When the user physically touches the resistive surface of the touch panel, relevant electrode segments at the touched position generate X- and Y-axis signals and a controller connected with the touch panel recognizes an intersection of positions indicated by the X- and Y-axis signals and calculates X and Y coordinates of the relevant touched position.
FIG. 1 is a plan view showing an example of a conventional touch panel. A touch panel generally has a disadvantage in that since a voltage gradient or voltage drop occurs from positions where electrodes are installed, to middle positions of X and Y axes, an electric field is distorted and thus linearity is distorted. In order to compensate the voltage gradient or drop, a touch panel 10 shown in FIG. 1 has a configuration in which a series of “Z-shaped” electrode segments 12, 14 is curved inwardly from corners of the touch panel to middle positions of four sides of the touch panel and “T-shaped” electrode segments 16 are disposed just in the middle portions of the four sides to compensate the voltage drop. Further, electrode segments 18 are connected to each other at the corners of the touch panel 10. Although not shown in the figure, lead wires for supplying electric power are connected to the electrode segments 18 at the corners.
However, there is a problem in such a touch panel 10 in that the size of an active area of the touch panel 10 is decreased and linearity of equipotential lines is not easily secured with the configuration of the electrode segments curved inwardly. Further, there is a difficulty in fabricating the electrode segments of which the series is curved.
FIG. 2 is a plan view showing an example of another conventional touch panel. In a touch panel 40 shown in FIG. 2, electrode segments 42, 44 with irregular geometric shapes such as “I,” “T,” and “L” are arranged in rows along four sides of the touch panel but they are not connected to one another at corners of the touch panel 40.
However, even in such a touch panel 40, a potential distortion phenomenon occurs and there exist areas 46 where a voltage gradient or voltage drop occurs from positions where the electrode segments are installed, to middle positions of X- and Y-axes of the touch panel, due to the electrode segments 42, 44 with the irregular geometric shapes. Thus, the size of an active area 48 is decreased and there is a difficulty in securing linearity of equipotential lines, in the same way as the touch panel shown in FIG. 1. Further, since the geometric electrode segments 42, 44 shown in FIG. 2 should be fabricated through processes of deposition, etching and the like, there is a difficulty in fabricating them.